Bimetallic element



April 10, 1928. 1,665,935

. H. SCOTT BIMETALLIC ELEMENT Filed Dec. 27. 1926 Fig. 1.

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i1 5. BY

TTORN EY Patented Apr. 10, 1928.

UNITED STATES PATENT OFFICEL HOWARD SCOTT, 01' WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO. WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

IBIMETALLIC ELEMENT.

Application filed December My invention relates to thermostatic devices and particularly to bimetallic elements therefor.

An object of my invention is to provide 8 a bimetallic element for thermostatic devices that has no appreciable deflection at relatively low temperatures.

Another object of my invention is to provide a bimetallic element for thermostatic 1 devices that has a high temperature coefficient of expansion at relatively high temperatures.

In practicing my invention, I provide a metallic element for thermostatic devices that is composed of two cooperating alloys joined together in any suitable manner. The alloy having the high temperature coeflicient of expansion is composed of manganese, nickeland iron, and the alloy com- 0 prising the low expansion element is composed of nickel and iron with minor proportions of impurities.

The'two alloys which cooperate to form the bimetallic element have substantially 2 the same coeflicients of expansion at normal temperatures but at relatively high temperatures ,the difference in the expansion of the two alloys is very pronounced and uniform over a temperature range of about 200 C. Therefore, the bimetal is not eifective as a thermostatic deviceat normal tem-' peratures but is efiective at relatively high temperatures. An advantage in utilizing a bimetal of this character for thermostatic purposes is that the stresses in the bimetal are practically nil at relatively low temperatures and greatly reduced in the operating range of temperatures to which the bimetal is subjected. This advantage facili- 40 tates the ease with which the bimetal referred to maybe manufactured.

Pure iron when heated gradually to high temperatures passes through a transformation point at about 900 C., and through a second transformation point at approxi- .mately 1400 C. From ordinary temperatures to 900 (1, pure iron expands uniformly and has a temperature COBl'llClQIlt of expansion approximately equal to 12 10' centimeters per 0., but above 900 C., the

crystalline structure of the iron becomes austenetic in character and the expansion thereof is greatly increased. Between 900 27, 1926. Serial No. 157,320.

C. and l40 0 (1, the temperature coefficient of pure 11'011 is approximately 20 10' centimeters 'per C.

I have found that nickel and manganese when properly alloyed with pure iron profoundly changes the temperature-expansion characteristics thereof, in that the temperature-expansion characteristics of the ,austenetic iron is lowered to the region of temperatures to which bimetal is ordinarily sub ected. Manganese isparticularly useful in this alloy, because of the fact that the transformation point of pure iron which occurs at about 900 C. is lowered in some instances to temperatures below that of liquid air. The function of the nickel is to introduce a pronounced reversible change in the coefficient of expansion such that the coeflicient is law and substantially the same as that of a low expansion alloy, for instance a nickel-iron-alloy, at low tem eratures, but very much higher at relatively high temperatures.

I have found also that a bimetal composed of a ferrous alloy containing 38% nickel and 4.6% manganese, and a cooperating ferrous alloy containing substantially 42% nickel is very useful in the temperature range extending between 200 C. and substantially 400 C. .From 0 C. to 200 0., this bimetal has, for practical purposes, a zero' temperature coeflicient of deflection or bending.

In the single sheet of drawings, Fig. 1 illustrates the temperature expansion characteristics of a manganese-nickel-iron alloy, a nickel iron alloy and the difierence in expansion between these alloys, and I Fig. 2 illustrates the temperature expansion characteristics of a modified nickelmanganese alloy,"a nickel iron alloy and the difference in expansion between these alloys.

The ordinates of the curvesillustrated in Figs. 1 and 2 of the drawings represent expansion in thousandths per unit length, and the abscissae represent temperature in degrees centigrade.

In Fig. 1 of the drawings, a curve 11 represents the temperature expansion characteristics of a high expansion ferrous alloy containing nickel and manganese, and curve 12' represents the temperature expansion characteristics of. a relatively low expansion 42% nickel-iron alloy. Curve 13 represents the temperature deflection or bending characteristic of a bimetallic strip composed of alloysrepresented by curves 11 and 12.

In Fig. 2 of the drawings, curve 14 illustrates the temperature expansion characteristic of a high expansion ferrous alloy containing nickel and manganese in different proportions than in the alloy represented by the curve 11. Curve 15 illustrates the temperature expansion vcharacteristics of a 42% nickel-iron alloy, and curve 16 illustrates the temperature characteristic of a bimetallic strip made by suitably joining together strips of the alloys represented by curves 14 and 15.

The expansion of the alloy represented by the curve 11 increases gradually from 0 C. to approximately 100 (1, but from 100 C. to temperatures higher than 400 0., the expansion thereof takes place at a much higher rate and is substantially uniform.

The expansion of the alloy represented by curve 12 is substantially uniform from 0 C. to 300 0., but at temperatures above 300 (1, the expansion increases very rapidly. Curve 13 illustrates the expansion of a bimetal composed of the alloys 11 and 12.

and it is to be noted that from 0 C. to about 100 (3., the expansion thereof is not appreciable, but from 100 C. to substantially 350 0., the expansion is quite uniform and takes place at a rapid rate. The temperature coeflicient "of expansion between these latter temperatures is relatively high, and in fact is higher than the expansion characteristics of a bimetal composed of monel metal and a nickle steel. The alloy corresponding to the curve 12 is particularly useful for controlling temperatures between 150 C. and 350 C. Below 105 C. the expansion is not so great and, therefore, when the device is inoperative, the stresses in metal are reatly reduced, thereby tending to increase t 1e useful life thereof.

In Fig. 2 of the drawings, the nickel-manganese-iron alloy illustrated by curve 14 differs in the manganese nickel content of the alloy illustrated by curve 11 of Fig. 1. It is to be noted that between 0 C. and 200 C. the expansion of this metal does not differ appreciably from the expansion of, the 42% nickel steel alloy. This is particularly evident in the curve 16, in that the portion thereof between 0 C. and 200 C. is substantially flat and lies a little below the zero expansion line. In fact the bimetal between these temperatures reverses its curvature slightly. From 200 C. to 400 C. the metal expands at arelatively high rate. Its temperature coeiiicient of expansionis particularly high between these temperatures.

The nickel content of the alloys designated by curves 11 and 14 may vary between the limits of substantially 15% and 40%, and the manganesecontent between the limits of substatially 1% and 8%.

The nickel content of the alloys illustrated by curves 12 and 15 may vary between the limits of substantially 38% and 45%.

It is to be understood that, while curves 13 and 16 represent the temperature deflection or bending characteristics of a bimetal in which the low expansion alloy is a nickeliron alloy containing about 42% nickel, I may utilize any other low expansion metallic element Whose temperature characteristics, as well as its strength and ductility, are suitable to produce a bimetallic strip having as its high expansion element an alloy ofmanganese, nickel and iron as herein set forth.

A bimetal composed of the alloys illustrated by curves 14 and 15, is particuiarly useful between the range of 200 C. and 400 0., as this is its most sensitive range to changes in temperature. When this bimetal cools to below 200 0., the temperature coeiiicients of expansion of the two metals are substantially equal, thereby reducing the stresses between them below this temperature. The manganese nickel content of the high expansion alloy may be varied in accordance with the temperature range that a bimetal in which it forms one of the co operating elements is to be subjected. As the deflection of a bimetal corresponding to curve 13 is very low at 150 C. the stresses which are directly proportional to the deflection are relatively low and substantially nil for practical purposes. This phenomena is desirable for it reduces the stresses at relatively high temperatures and'permitsthe bimetal to be used at these temperatures 5 Without sacrifice of sensitivity.

By my invention I have provided abimetallic element that is free from the irreversible characteristics at the temperatures to which it is to be subjected, and which is relatively 110 inactive at temperatures to which it is to be non-responsive. This'bimetal is very sensitive, however, in the range of temperatures to which it is to be applied.

I Various modifications may be made in the 115 device embodying my invention Without departing from the spirit and the scope of my invention. I desire therefore that only such limitations shall be placed thereon as are imposed by the prior art and the appended 120 claims.

Iclaim as my invention:

1. A thermostatic element comprising two cooperating elements having diflerent temperature coefficients of expansion, one of said 125 elements being a ferrous alloy containing substantially 42% nickel, and the other element being a ferrous alloy containing not less than 1% manganese, and nickel.

2. A thermostatic element-comprising two cooperating elements having different temperature coefficients of expansion, one of said elements being a ferrous alloy containing substantially 42% nickel, and the other element being a ferrous alloy containing nickel and substantially 8% manganese.

.3. A thermostatic device comprising two cooperating elements having different temperature coefficients of expansion, one of said elements being *a ferrous alloy containing 42% nickel, and the other of said elements being an alloy containing from 15 to 40% ofnickel and from 1% to 8% of manganese.

4. A thermostatic device comprising two metals having different temperature coefiicients of expansion, one of said elements being a ferrous alloy containing 38% to 45% nickel and the other of said elements being a ferrous alloy containing from 32% to 38% of nickel and from 3.5% to 4.6% of manganese.

5. A-thermostatic device comprising two metals having different temperature coefiicients of expansion, one of said elements being a ferrous alloy containing substantially 42% nickel and the other of said elements being a ferrous alloy containing substantially 4.6% of maganese and substantially 38% of nickel.

In testimony whereof, I have hereunto subscribed my name this 21st day of December, 1926.

HOWARD SCOTT. 

